One old guy dying thinks of not only his life but that of his father, also dead. We the reader get to see more of both their lives than they share with each other. That's it for the story - oh, it's buttered up with quotes from a fictional clock repair manual, but the metaphor of a "life running down" doesn't fit either of the men, and feels very forced.
With a little more focus, this could have been a very good book about dying and clocks winding down, or a very good book about the similarities of father and son - but instead we get a mish-mash. The Pulitzer guys liked it, but I didn't.